Abstract: A rotary fluid flowmeter device comprising a casing enclosing a chamber bounded partly by a fluid-tight but magnetically permeable partition, said chamber having an inlet and an outlet for the fluid of which the flow is to be metered, and a rotor having radially-directed, axially-extending blades being borne for rotation within the chamber, wherein in operation fluid entering the chamber through the inlet is directed towards and impinges upon the rotor blades to cause rotation of the rotor, and wherein the casing houses an electronic sensing circuit on the far side of the partition from said chamber, the circuit being adapted to produce an electronic pulse train the rate of which represents the rate of rotation of the rotor.